During semiconductor wafer processing, wafers are coated with polyimide at various points in the process. A layer of uncured polyimide is first applied on a wafer using a polyimide apply tool, such as a spin-apply tool. The polyimide layer is, then, cured by baking the wafer at an appropriate curing temperature in a cure bake oven.
In many semiconductor wafer manufacturing systems, the polyimide apply tool and the cure bake oven are separate equipment and the wafers are transferred from the polyimide apply tool to the cure bake oven by an automated wafer-transfer robot. During a typical manufacturing operation, it may be necessary to stop or pause the operation of the wafer-transfer robot for various reasons. When the wafer-transfer robot is paused, some wafers may get stranded either on the polyimide apply tool after the uncured polyimide has been applied or stranded in transit between the polyimide apply operation and the baking operation. This pause between the polyimide apply operation and the baking operation is usually detrimental to the quality of the as-cured polyimide coating layer and further causes delays in wafer processing. To ensure good quality polyimide coating, preferably the polyimide coating should be bake cured as soon as possible after the polyimide apply operation. When the process is interrupted between the polyimide apply step and the curing step, detrimental defects in the polyimide coating often results causing the affected wafers to be scrapped. This problem is common for most polyimides used in the semiconductor industry. Thus, when the wafer-transfer robot is paused or stopped, stranding wafers between the polyimide apply operation and the cure bake operation, it would be desirable to monitor the length of the pause or stoppage time. However, the polyimide coating tools currently being used in the industry do not provide the means for monitoring the stoppage time.